The disclosure of U.S. Provisional Application No. 61/575,486, filed Aug. 22, 2011, is hereby incorporated herein in its entirety by reference.
It is common for harvester customers and operators to desire increased capacity and productivity from their harvesters. However, chassis configurations limit the area available for increasing cleaning sieve size. Increasing width is typically the easiest manner of increasing sieve size. However, many jurisdictions limit overall vehicle width and weight which places a limitation of the extent of increase possible. Also, cost is a constraint as is power train capacity.
Another avenue for increasing productivity is to reduce material other than grain or MOG that reaches the cleaning system, referred to as pre-separation. However, this approach has limitation for some grains and harvesting conditions, e.g., most effective when the difference between terminal velocity of the grain and that of the MOG is greatest. Another constraint is that increasing pre-separation increases space required for that process, and this space must come from other systems such as the threshing or separation system for separating grain from larger MOG.
The cleaning system of a combine harvester typically includes at least one fan operable for directing a flow of air upwardly and rearwardly through at least two sieves reciprocatingly moving in at least one plane of motion. This general configuration provides a winnowing action to mechanically and pneumatically separate the less dense MOG from the denser grain. More specifically many known harvesters use a fan and split ducts to direct the flow of air through a forward pre-cleaning duct to a grain cascading area having a first or pre-sieve for removing some of the MOG, and through a second or rear duct to the main cleaning sieves including a first or upper sieve or chaffer, and a second or lower cleaning sieve through which all of the clean grain passes en route to a clean grain conveyor which carries the cleaned grain to a holding tank or other container.
What is sought is a manner of increasing grain handling capacity for known cleaning system configurations, which does not require space from other systems, does not significantly increase the cleaning system size, and overcomes one or more of the shortcomings and limitations set forth above.